The present invention relates generally to a head stack assembly (“HSA”) that supports and drives a head and a magnetic disc drive having the HSA, and more particularly to a connection between a suspension and an arm in the HSA. The present invention is suitable, for example, for a manufacture of the HSA used for a hard disc drive (“HDD”).
Along with the recent spread of the Internet etc., demand for recording a large amount of information including motion and still pictures have increased. Therefore, a large-capacity magnetic disc drive, such as HDD, has increasingly required. The HDD typically includes a disc on which a magnetic material is adhered, and a HSA that supports a head and moves the head to a target position on the disc. The HSA includes a carriage (also referred to as an “actuator”, an “E-block” due to its E-shaped section or “actuator (“AC”) block”), a suspension attached to a support portion of the carriage (referred to as an “arm” hereinafter), a magnetic head part supported on the suspension, and a base plate that attaches the suspension to the arm. The magnetic head part includes a fine head core (simply referred to as a “head” hereinafter) that records and reproduces a signal, and a slider that supports the head.
The suspension also serves as a flat spring that compresses the slider against the disc at a predetermined compression force. As the disc rotates, the airflow or air bearing occurs between the slider and the disc, and floats the slider from the disc surface. The floating slider is spaced from the disc by a predetermined distance due to a balance between the floating force and the compression force. In this state, the arm rotates and moves the head to (seek for) a target position on the disc, for information reading and writing.
A recent high-density disc requires high head positioning precision, and thus the HSA should be manufactured precisely. For example, when the suspension warps or twists due to the manufacturing errors, the compression force, the flying height, the orientation and vibration tolerance may vary from the designated values, and the positioning accuracy deteriorates.
In the HSA, the suspension and base plate are laser-welded to each other, whereas the base plate is swaged or caulked with the arm. The swaging is the way of jointing the base plate with the arm by crushes or plastically deforms part of the base plate against the arm. The swaged base plate and arm are separable when a sharp member is inserted between them, and improves the economical efficiency of the magnetic disc drive, because when the suspension and the magnetic head part are defective, it is sufficient to replace only the base plate side instead of the entire HSA.
However, the force for the plastic deformation to the base plate causes a deformation of the base plate, such as warp, and deteriorates the head positioning accuracy. One proposed method that reduces the deformation of the base plate is to form a thin-walled section between the part of the base plate that receives a deformative force and a joint of the suspension and to reduce the influence of the deformation of the base plate on the suspension. See, for example, Japanese Patent Application, Publication No. 7-192420.
The instant inventors have discovered that the deformation of the base plate results from a superposition between base plate's own deformation due to a plastic deformation force, and arm's deformation. Japanese Patent Application, Publication No. 7-192420 that attempts to prevent only the former cannot sufficiently reduce the influence of the arm's deformation on the base plate. In addition, Japanese Patent Application, Publication No. 7-192420 arranges the thin-walled section on the arm, and poses a problem that the lower base plate warps downwardly. This is because the thin-walled section reduces the rigidity of the base plate at the suspension side and the base plate is likely to deform due to the gravity and vibrations during swaging. Since the arm supports part of the base pate at the suspension side from the thin-walled section, the problem associated with the upper base plate can be solved to some extent. On the other hand, there is no support member under the lower base plate, and the deformation becomes conspicuous.